x^2-0.8x-0.64=0

Solution for x^2-0.8x-0.64=0 equation:

x^2-0.8x-0.64=0

a = 1; b = -0.8; c = -0.64;
Δ = b2-4ac
Δ = -0.82-4·1·(-0.64)
Δ = 3.2
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-0.8)-\sqrt{3.2}}{2*1}=\frac{0.8-\sqrt{3.2}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-0.8)+\sqrt{3.2}}{2*1}=\frac{0.8+\sqrt{3.2}}{2}
$